World number one Caroline Wozniacki did little to silence her critics Wednesday as she struggled to win her singles match in Denmark's 2-1 loss to Bulgaria at the mixed teams Hopman Cup in Perth. The Dane, who is clinging to the top ranking in women's tennis by 115 points and has been much maligned for failing to win a Grand Slam, made a host of unforced errors in her marathon clash against Bulgaria's Tsvetana Pironkova. Wozniacki's grinding 7-5, 4-6, 6-2 win in 144 minutes against her 46th-ranked opponent gave Denmark the lead in the Group A tie, but Bulgaria's Grigor Dimitrov squared the ledger defeating Frederik Nielsen, 7-6 (7/5), 6-2. The Bulgarians then came from a set down to win the deciding mixed doubles in a match tiebreak, 3-6, 6-4, 10-1, and keep their Hopman Cup hopes alive. Denmark can still reach the final if they beat the Czech Republic in their final tie on Friday, when Wozniacki will face her first big test of 2012 against world number two Petra Kvitova. It was hoped Wozniacki would produce a more compelling singles performance than in her opening outing in Perth, where she had battled from 5-1 down in the first set to beat 55th-ranked American Bethanie Mattek-Sands in straight sets. After the marathon match, the Dane played down her error-riddled performance, saying Pironkova was a tricky opponent. "The most important thing is to win," she said, adding that she was confident of improving dramatically ahead of the Australian Open. "I always think I am improving, but the first couple of matches of the season are always a bit tough and you need to find your feet our there. "As I keep playing more matches I will improve and start playing better." Pironkova had many chances in the first set against the Dane but, as in her loss to Kvitova on Monday, she could not capitalise and often retreated back into a defensive approach when opportunity beckoned. It allowed Wozniacki, who relied on her defensive game throughout and hit few winners against Pironkova, to steady when the pressure was on. Pironkova was rewarded for more aggression in the second set and squared the match, but Wozniacki overcame a code violation for coaching in the third set to claim the match. The Bulgarian ultimately paid the price for her unforced errors, while Wozniacki was again rewarded for her undoubted ability to scramble under pressure.